Hitherto, a seat belt apparatus installed on a seat of a vehicle, such as an automobile, restricts the occupant with a seat belt constituted by webbing in times of emergency (hereinafter, merely referred to as in an emergency), such as vehicular collision in which deceleration that is substantially larger than deceleration occurring during normal traveling acts on the vehicle. Generally, such a seat belt apparatus is provided with a seat belt retractor. Many of the conventional seat belt retractors include a vehicle sensor that stops withdrawal of the seat belt by being operated upon a large deceleration in an emergency, and a webbing sensor that stops withdrawal of the seat belt by being operated when the seat belt is rapidly drawn out at a rate that is higher than the normal seat belt withdrawal rate in order to fasten the seat belt, for example (in other words, with an acceleration of withdrawal that is larger than a normal acceleration of withdrawal when fastening the seat belt).
Incidentally, for example, there are cases in which the vehicle sensor is operated by vibration or the like while the vehicle is travelling even in a seat belt apparatus or the like that is installed on a vehicle seat on which no occupant is sitting and in which the seat belt is not fastened thereto. However, there are cases in which cancellation (incapacitation) of the intrinsic function of the vehicle sensor, which is the vehicle sensor not operating except for when the seat belt is fastened around the occupant and stopping the withdrawal of the seat belt by being operated in an emergency, is desired. Accordingly, a seat belt retractor that exerts the intrinsic function of the vehicle sensor described above when in a state in which the seat belt is fastened around the occupant and, further, that cancels (incapacitates) the intrinsic function of the vehicle sensor at a predetermined condition, other than when the seat belt is fastened around the occupant, that has been set in advance has been proposed (see PTL 1, for example).
The seat belt retractor described in PTL 1 includes a ring gear that integrally rotates with a spool, and a control lever. In a state in which the seat belt is withdrawn by a predetermined amount from the seat belt retractor, the ring gear does not allow the control lever to operate; accordingly, the control lever permits the vehicle sensor to operate and enables the intrinsic function of the vehicle sensor to be exerted. Furthermore, the ring gear that rotates in accordance with the rotation of the spool in the seat belt retraction direction operates the control lever; accordingly; in a state in which the spool, at least, retracts the total amount of the seat belt, the control lever stops the operation of the vehicle sensor such that the intrinsic function of the vehicle sensor is cancelled.
Meanwhile, there are cases in which the webbing sensor is operated even in a case other than the rapid seat belt withdrawal and stops the withdrawal of the seat belt from the seat belt retractor. For example, when the total amount of the seat belt that has been withdrawn is retracted, there are cases in which a so-called end lock occurs, which makes normal withdrawal of the seat belt difficult, by unintended operation of the webbing sensor.
Accordingly, in order to prevent such an end lock caused by the belt withdrawal sensor, a seat belt retractor has been proposed (see PTL 2, for example) that cancels (incapacitates) the intrinsic function of the webbing sensor that is operated and stops the withdrawal of the seat belt when the total amount of the seat belt is retracted.
The seat belt retractor described in PTL 2 includes an inertia plate that swings upon rapid seat belt withdrawal, a webbing sensor gear that is rotatably provided and that includes internal teeth and external teeth, a webbing sensor pawl that is operated upon swinging of the inertia plate and that engages with an internal tooth of the webbing sensor gear, and a gear rotation control pawl that stops the rotation of the webbing sensor gear by engaging with an external tooth of the webbing sensor gear.
In the seat belt retractor described in PTL 2, in a state in which the seat belt is withdrawn by a predetermined amount from the seat belt retractor, the gear rotation control pawl engages with an external tooth of the webbing sensor gear and makes the webbing sensor gear non-rotatable. With the above, when the webbing sensor pawl is operated upon swinging of the inertia plate and is engaged with an internal tooth of the webbing sensor gear, the webbing sensor gear does not rotate; accordingly, the intrinsic function of the webbing sensor is exerted and the withdrawal of the seat belt is stopped. Furthermore, when in a state in which the spool has retracted substantially the total amount of the seat belt, the gear rotation control pawl is separated from the external teeth of the webbing sensor gear and allows the webbing sensor gear to rotate. With the above, even if the webbing sensor pawl is operated upon swinging of the inertia plate and is engaged with an internal tooth of the webbing sensor gear, since the webbing sensor gear rotates and the spool becomes rotatable in the seat belt withdrawal direction, the intrinsic function of the webbing sensor is cancelled. Accordingly, withdrawal of the seat belt can be performed and end lock is prevented. Note that in the seat belt retractor described in PTL 2, a vehicle sensor is provided as well.